In the current study the investigators tested the hypothesis that prescribing letrozole as an ovulation induction agent in infertile women would increase pregnancy rate, ovulation and follicle number (at the normal size range of 18-24 mm), endometrial thickness (to normal thickness of 6 mm) and not have considerable side effects in the patients. The primary outcome measure was normal follicular size and the secondary outcome measure were the clinical and current pregnancy rates. Clinical pregnancy was considered as the presence of a gestational sac with fetal heart activity. Letrozole tablets were prescribed by an experienced nurse who throughly explained the method of use to the patients. Sonography was done by an experienced radiologist.